ABSTRACT:
For railway traction drives, the active front end
usually adopts a single-phase rectifier. However, the dc-link voltage of this
single-phase rectifier contains a second-order fluctuating component due to the
fluctuation of the instantaneous power at both the ac and dc sides. Fed by the
fluctuating dc-link voltage, the traction motor suffers from severe torque and
current pulsation. The hardware solution with an additional LC resonant
filter is simple, but it will reduce the power density of the system. An
alternative solution is to eliminate the beat component in the stator
voltage/current through modulation ratio or frequency compensation. However, it
is difficult to achieve high performance for the conventional feedforward method.
In this paper, an improved closed-loop torque and current pulsation suppression
method is proposed, which can eliminate the q-axis current pulsation
component in the field-oriented control system through frequency compensation.
The torque pulsation suppression is also achieved automatically. Simulation and
experimental results show that the proposed scheme can effectively reduce the
torque and current pulsation in various operation modes compared with the
conventional feedforward method.
KEYWORDS:
1.
Fluctuating
dc-link voltage
2.
q-axis current pulsation
3.
Suppression
4.
Torque
pulsation
5.
Traction drive
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. Circuit schematic of the ac/dc/ac traction drive system.
EXPECTED SIMULATION RESULTS:
Fig.
2. Simulation results of two methods in the asynchronous modulation mode. (a)
Line voltage of the motor. (b) and (c) Stator current and torque with the conventional
method. (d) and (e) Stator current and torque with the proposed method. (f)
DC-link voltage of the inverter without and with the proposed method.
(g)
Transition waveforms of the stator current without and with the proposed
method.
Fig.
3. Spectrum analysis of the simulation results of the two methods in the
asynchronous modulation mode. (a)–(c) Stator current without compensation, with
the conventional method, and with the proposed method. (d)–(f) Torque without
compensation, with the conventional method, and with the proposed method.
Fig.
4. Simulation results of the two methods in the synchronous modulation mode.
(a) Line voltage of the motor. (b) and (c) Stator current and torque with the conventional
method. (d) (e) Stator current and torque with the proposed method.
Fig.
5. Simulation results of the two methods in the square-wave modulation mode.
(a) Line voltage of the motor. (b) and (c) Stator current and torque with the conventional
method. (d) and (e) Stator current and torque with the proposed method.
CONCLUSION:
A
closed-loop torque and current pulsation suppression method for railway
traction drives under fluctuating dc-link voltage is proposed. This method aims
to eliminate the q-axis current pulsation component in the FOC system
through output frequency compensation. The torque pulsation suppression is
achieved on the basis of q-axis current pulsation elimination automatically.
A resonant controller is proposed for the closed loop control of q-axis
current and dynamic compensation of the output frequency. Different from the
conventional feed forward open-loop frequency compensation method, the torque
pulsation with the proposed method is suppressed through the elimination of the
q-axis current pulsation component rather than the beat component in the
output voltage. The effectiveness of the proposed method have been verified by
simulation and experiments on traction drives with the inverter operated in
asynchronous, synchronous, and square wave modulation modes, respectively. The
results have been compared to those with the conventional feed forward
frequency compensation method based on fluctuating dc-link voltage detection. Both
simulation and experimental results show that the suppression of stator current
and torque pulsation are obvious in different modulation modes with the
proposed control method using the same dc-link capacitance.
The proposed suppression method can reduce the
sensitivity of the system to variations of the grid frequency. However, the fluctuating
component in the dc-link voltage will be increased with the proposed method
compared with the LC resonant filter solution.
REFERENCES:
[1] R. J. Hill, “Electric railway traction. II.
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[3] H. Ouyang, K. Zhang, P. Zhang, Y. Kang, and J.
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Aug. 2011.
[4] J. Klima, M. Chomat, and L. Schreier, “Analytical
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